Electrical and optical properties of ITO and ITO/Cr-doped ITO films

In this paper we report on the effects of the insertion of Cr atoms on the electrical and optical properties of indium tin oxide (ITO) films to be used as electrodes in spin-polarized light-emitting devices. ITO films and ITO(80 nm)/Cr-doped ITO(20 nm) bilayers and Cr-doped ITO films with a thickness of 20 nm were grown by pulsed ArF excimer laser deposition. The optical, structural, morphological and electrical properties of ITO films and ITO/Cr-doped structures were characterized by UV–Visible transmission and reflection spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Hall-effect analysis. For the different investigations, the samples were deposited on different substrates like silica and carbon coated Cu grids. ITO films with a thickness of 100 nm, a resistivity as low as ～4×10^?4 Ω?cm, an energy gap of ～4.3 eV and an atomic scale roughness were deposited at room temperature without any post-deposition process. The insertion of Cr into the ITO matrix in the upper 20 nm of the ITO matrix induced variations in the physical properties of the structure like an increase of average roughness (～0.4–0.5 nm) and resistivity (up to ～8×10^?4 Ω?cm). These variations were correlated to the microstructure of the Cr-doped ITO films with particular attention to the upper 20 nm.     

Effect of the duty ratio on the indium tin oxide (ITO) film deposited by in-line pulsed DC magnetron sputtering method for resistive touch panel

The indium tin oxide (ITO) film was deposited on PET (polyethylene terephthalate) film using in-line pulsed DC magnetron sputtering system with different duty ratios. The reverse time and the frequency of pulsed DC power were changed to obtain the different duty ratios. From the electrical and optical properties such as the sheet resistance, resistivity, thickness and transmittance, the pulsed DC sputtered ITO/PET films were also superior to the DC sputtered ITO/PET films. The reverse time had little effect on the properties of the ITO/PET film and the frequency of pulsed DC power had an immerse effect on the properties of the ITO/PET films. The optimal ITO/PET film was obtained when the frequency was 200 kHz, the reverse time was 1 μs, and the duty ratio was about 80%.     

Thermal induced changes of lead zirconium titanate films and their consequences for liquid crystal devices applications

Thin films of lead zirconate titanate (PZT) were obtained by a modified sol–gel route on float glass and indium tin oxide (ITO)-covered float glass substrates. Different thermal treatments were performed on the deposited films in the temperature range 100–700°C. Spectroscopic ellipsometry was used to investigate the optical properties of the deposited films, and the changing optical absorption spectra were interpreted in terms of the growth of two different crystal phases, pyrochlore and ferroelectric perovskite, as a function of annealing temperature. Moreover, a specific resonance at 1.9 nm was detected when thin PZT films are deposited on ITO substrates and was attributed to a particular charge distribution at the interface. Finally, the performance in rectifying the electro-optical response of asymmetric nematic liquid crystal cells was tested for some of the films undergoing different thermal treatments.     

Low temperature deposition of transparent conducting ITO/Au/ITO films by reactive magnetron sputtering

Transparent conducting indium tin oxide/Au/indium tin oxide (ITO) multilayered films were deposited on unheated polycarbonate substrates by magnetron sputtering. The thickness of the Au intermediated film varied from 5 to 20 nm. Changes in the microstructure, surface roughness and optoelectrical properties of the ITO/Au/ITO films were investigated with respect to the thickness of the Au intermediated layer. X-ray diffraction measurements of ITO single layer films did not show characteristic diffraction peaks, while ITO/Au/ITO films showed an In₂O₃ (2 2 2) characteristic diffraction peak. The optoelectrical properties of the films were also dependent on the presence and thickness of the Au thin film. The ITO 50 nm/Au 10 nm/ITO 40 nm films had a sheet resistance of 5.6 Ω/□ and an average optical transmittance of 72% in the visible wavelength range of 400-700 nm. Consequently, the crystallinity, which affects the optoelectrical properties of ITO films, can be enhanced with Au intermediated films.     

Optical emission spectroscopy during fabrication of indium-tin-oxynitride films by RF-sputtering

Indium-tin-oxide (ITO) and indium-tin-oxynitride (ITON) films have been deposited on glass by rf-sputtering from an ITO target, using Ar plasma and N₂ plasma, respectively, and different rf-power. Optical emission spectroscopy (OES) was employed to identify the species present in the plasma and to correlate them with the properties of the ITO and ITON thin films. Emission lines of ionic In could only be detected in N₂ plasma, whereas in the Ar plasma additional lines corresponding to atomic In and InO, were detected. The deposition rate of thin films was correlated with the In species, rather than the nitrogen species, emission intensity in the plasma. The higher resistivity and lower carrier concentration of the ITON films, as compared to the respective properties of the ITO films, were attributed to the incorporation of nitrogen, instead of oxygen, in the ITON structure.     

Room temperature deposition of crystalline indium tin oxide films by cesium-assisted magnetron sputtering

Indium tin oxide (ITO) films were deposited on a Si (1 0 0) substrate at room temperature by cesium-assisted magnetron sputtering. Including plasma characteristics, the structural, electrical, and optical properties of deposited films were investigated as a function of cesium partial vapor pressure controlled by cesium reservoir temperature. We calculated the cesium coverage on the target surface showing maximum formation efficiency of negative ions by means of the theoretical model. Cesium addition promotes the formation efficiency of negative ions, which plays important role in enhancing the crystallinity of ITO films. In particular, the plasma density was linearly increased with cesium concentrations. The resultant decrease in specific resistivity and increase in transmittance (82% in the visible region) at optimum cesium concentration (4.24 × 10⁻⁴ Ω cm at 80 °C of reservoir temperature) may be due to enhanced crystallinity of ITO films. Excess cesium incorporation into ITO films resulted in amorphization of its microstructure leading to degradation of ITO crystallinity. We discuss the cesium effects based on the growth mechanism of ITO films and the plasma density.     

ITO/Au/ITO multilayer thin films for transparent conducting electrode applications

Transparent and conducting ITO/Au/ITO multilayered films were deposited without intentional substrate heating on polycarbonate (PC) substrate using a magnetron sputtering process. The thickness of ITO, Au and ITO metal films in the multilayered structure was constant at 50, 10 and 40 nm, respectively.Although the substrate temperature was kept constant at 70 °C, ITO/Au/ITO films were polycrystalline with an (1 1 0) X-ray diffraction peak, while single ITO films were amorphous. Surface roughness analysis indicated ITO films had a higher average roughness of 1.76 nm, than the ITO/Au/ITO film roughness of 0.51 nm. The optoelectrical properties of the ITO/Au/ITO films were dependent on the Au thin film, which affected the ITO film crystallinity. ITO/Au/ITO films on PC substrates were developed with a resistivity as low as 5.6 × 10⁻⁵ Ω cm and a high optical transmittance of 71.7%.     

Optimum packing density and crystal structure of tin-doped indium oxide thin films for high-temperature annealing processes

The influence of high-temperature annealing on the electrical properties and microstructure of tin-doped indium oxide (ITO) thin films was investigated as a function of oxygen gas flow ratio to argon gas during the sputtering deposition. The ITO thin films were annealed at 500 °C in air after the deposition. It was found that the ITO thin films, which were deposited in relatively low oxygen gas flow ratio, exhibited high Hall mobility and low-resistivity after the annealing. Furthermore, the X-ray reflectivity and diffraction measurement revealed that the ITO thin film with low-resistivity after annealing exhibited high packing density, smooth surface and low crystallization degree. It can be considered that the carrier electron scattering was suppressed with increasing in the packing density of the ITO thin film; as a result, the Hall mobility and resistivity were improved.     

Electrical and optical properties of Si-doped indium tin oxides as transparent electrode and anti-reflection coating for solar cells

We have studied the electrical and optical properties of Si-doped indium tin oxides (ITSOs) as transparent electrodes and anti-reflection coatings for Si-based solar cells. The ITSO thin films were obtained by co-sputtering of ITO and SiO₂ targets under target power control. The resistivity of the ITSO thin films deposited at 0.625 in terms of power ratio (ITO/SiO₂) were 391 Ωcm. In this condition, the ITSO thin films showed very high resistivity compared to sputted pure ITO thin films (1.08 × 10⁻³ Ωcm). However, refractive index of ITSO thin films deposited at the same condition at 500 nm is somewhat lowered to 1.97 compared to ITO thin films (2.06). The fabricated graded refractive index AR coatings using ITO, ITSO, and SiO₂ thin films kept over 80% of transmittance regardless of their thickness varing from 97 nm to 1196 nm because of their low extinction coefficient. As the AR coating with graded refractive indices using ITO, ITSO, and SiO₂ layers was applied to general silicon-based solar cell, the current level increased nearly twice more than that of bare silicon solar cell without AR coating.     

Thickness dependence of electrical properties of ITO film deposited on a plastic substrate by RF magnetron sputtering

Indium tin oxide (ITO) films with various thicknesses in range of 40-280 nm were prepared onto a plastic substrate (PMMA). Deposition was carried out with RF magnetron sputtering method and the substrate temperature was held at ∼70 °C, in lack of the thermal damage to the polymer substrate. Changes in microstructure and electrical properties of ITO films according to their thicknesses were investigated. It was found that amorphous layer with thickness of 80 nm was formed at the interface on the polymer substrate and polycrystalline ITO could be obtained above the thickness. Conductivity of ITO films was found to be strongly dependent on the crystallinity. Consequently, it is suggested that crystallinity of the deposited films should be enhanced at the initial stage of deposition and the thickness of amorphous region be reduced in order to prepare high quality ITO thin films on polymer substrates.     

The influence of the substrate nature on the iron repartition in the titania matrix

Fe-doped titania films were deposited by RF sputtering onto different substrates (glass and ITO/glass) in the same deposition run. The rutile nanocrystalline structure of Fe-doped thin films deposited on glass substrates and anatase nanocrystalline structure of Fe-doped thin films deposited on ITO/glass substrates were evidenced by XRD. SEM investigations showed a smooth surface with a dense nanostructure. XPS study evidenced an almost stoichiometric composition with different iron contents. EPR and XPS studies evidenced that iron entered into TiO₂ lattice by substitution, as isolated and dimer species. In Fe-doped thin films deposited on ITO/glass substrates the iron content is ten times higher than in Fe-doped thin films deposited on glass substrates and that a part of them entered as Fe²⁺.     

Properties of ITO films prepared by rf magnetron sputtering

Recently, a detailed study of the properties of ITO thin films deposited under various preparation conditions using the rf magnetron sputtering technique (from ITO target in pure Ar gas) has been undertaken in our laboratory. The effect of substrate temperature has been studied in a previous paper. Here the results of a study of the structural, electrical and optical properties of the ITO films with different thickness are presented. The figure of merit for the films, which is a measure of the quality of the films as transparent conductive layers for photovoltaic applications, has been evaluated.     

Fabrication of patterned polyaniline microstructure through microcontact printing and electrochemistry

Polyaniline (PANI) microstructures on ITO glass surface were achieved by microcontact printing of self-assembled film and electrochemical polymerization in an aqueous monoaniline solution. The patterned microstructures of PANI were easily transferred to an adhesive tape surface, which could be applied in the area of plastic circuit application. Optical microscope, atomic force microscopy (AFM), lateral force microscopy (LFM) and X-ray photoelectron spectroscopy (XPS) were used to examine the topography and properties of patterned PANI films. Optical microscope and AFM results showed that the PANI microstructure has regular pattern and clear boundary, while LFM and XPS results implied that this microstructure was completely covered by PANI. The data suggested that the interfacial properties of the surface control the rate of electrochemical polymerization, and the polymerization rate on the modified ITO surface is higher than that on the bare ITO area. In our experiments, cyclic voltammetric method, potentiostatic method and chronopotentiometry method were employed to deposited patterned PANI films on octadecyltrichorosilane modified ITO substrate.     

Properties of ITO–AZO bilayer thin films prepared by magnetron sputtering for applications in thin-film silicon solar cells

In this paper we study the electro-optical behavior and the application of indium–tin oxide (ITO) and aluminum-doped zinc oxide (AZO) bilayer thin films for silicon solar cells. ITO–AZO bilayer thin films were deposited on glass substrates using radio-frequency magnetron sputtering. The experimental results show that a decrease in the electrical resistivity of the ITO–AZO bilayer thin films has been achieved without significant degradation of optical properties. In the best case the resistivity of the bilayer films reached a minimum of 5.075×10^?4 Ω?cm when the thickness of the AZO buffer layer was 12 nm. The ITO–AZO bilayer films were applied as the front electrodes of amorphous silicon solar cells and the short-circuit current density of the solar cells was considerably increased.     

Thickness Dependence of Resistivity and Optical Reflectance of ITO Films

Indium-tin-oxide （ITO） films deposited on crystalline silicon wafer and Corning glass are prepared by directcurrent magnetron sputtering method at room temperature with various thicknesses. The thickness dependences of structure, resistance and optical refectance of ITO films are characterized. The results show that when the film thickness is less than 40 nm, the resistivity and optical reflectance of the ITO film changes remarkably with thickness. The optoelectrical properties trend to stabilize when the thickness is over 55 nm. The GXRD result implies that the ITO film begins to crystallize if only the thickness is large enough.     

Conducting properties of In2O3:Sn thin films at low temperatures

Electrical conductivity, Hall effect and magnetoresistance of In₂O₃:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, have been investigated in the temperature range 4.2–300 K. The observed temperature dependences of resistivity for films deposited at 230 °C as well as at nominally room temperatures were typical for metallic transport of electrons except temperature dependence of resistivity of the In₂O₃:Sn film deposited in the oxygen deficient atmosphere. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. It is established that changes of morphology and crystallinity of ITO films modify the low-temperature behavior of resistivity, which still remains typical for metallic transport. This is not the case for the oxygen deficient ITO layer. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of n-type ITO. That can explain lower n-type conductivity in this material crossing over to a Mott-type hopping at low temperatures. Results for the low temperature measurements of stoichiometric ITO layers indicate that they do not show any trace of metal-to-insulator transition even at 4.2 K. We conclude that, although ITO is considered as a highly doped wide-band gap semiconductor, its low-temperature properties are very different from those of conventional highly doped semiconductors.     

Rapid thermal annealing of ITO films

Tin-doped indium oxide (ITO) films with 200 nm thickness were deposited on glass substrates by DC magnetron sputtering at room temperature. And they were annealed by rapid thermal annealing (RTA) method in vacuum ambient at different temperature for 60 s. The effect of annealing temperature on the structural, electrical and optical properties of ITO films was investigated. As the RTA temperature increases, the resistivity of ITO films decreases dramatically, and the transmittance in the visible region increases obviously. The ITO film annealed at 600 °C by RTA in vacuum shows a resistivity of 1.6 × 10⁻⁴ Ω cm and a transmittance of 92%.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

Effect of substrate temperature on the growth of ITO thin films

Indium tin oxide (ITO) thin films were deposited onto glass substrates by rf magnetron sputtering of ITO target and the influence of substrate temperature on the properties of the films were investigated. The structural characteristics showed a dependence on the oxygen partial pressure during sputtering. Oxygen deficient films showed (4 0 0) plane texturing while oxygen-incorporated films were preferentially oriented in the [1 1 1] direction. ITO films with low resistivity of 2.05 × 10⁻³ Ω cm were deposited at relatively low substrate temperature (150 °C) which shows highest figure of merit of 2.84 × 10⁻³ square/Ω⋅     

Electrical and optical properties of indium tin oxide thin films grown by pulsed laser deposition

Indium tin oxide (ITO) thin films (200-400 nm in thickness) have been grown by pulsed laser deposition (PLD) on glass substrates without a post-deposition anneal. The electrical and optical properties of these films have been investigated as a function of substrate temperature and oxygen partial pressure during deposition. Films were deposited at substrate temperatures ranging from room temperature to 300 °C in O₂ partial pressures ranging from 0.1 to 100 mTorr. For 300 nm thick ITO films grown at room temperature in oxygen pressure of 10 mTorr, the electrical conductivity was 2.6᎒^-3 Q^-1cm^-1 and the average optical transmittance was 83% in the visible range (400-700 nm). For 300 nm thick ITO films deposited at 300 °C in 10 mTorr of oxygen, the conductivity was 5.2᎒^-3 Q^-1cm^-1 and the average transmittance in the visible range was 87%. Atomic force microscopy (AFM) measurements showed that the RMS surface roughness for the ITO films grown at room temperature was ~7 Å, which is the lowest reported value for the ITO films grown by any film growth technique at room temperature.